1. Field of the Invention
The present invention relates to a method for producing a drilling fluid from biomass-derived oils. More particularly, the present invention relates to a method for producing a drilling fluid in an estolide form from oils and fats derived from naturally occurring biomass.
2. Description of the Related Art
Although strictly managed by refineries, petroleum resources are still the greatest sources that pollute the Earth's environment. Extraction of petroleum resources results in the exposure of petroleum reserves, such as S, N, heavy metals, aromatics, and so on, deposited deep in the earth to the earth surface. Lubricants produced by refining petroleum resources are of low biodegradability and, when introduced into the ecosystem, are likely to greatly affect the ecosystem. In practice, ecological disturbance frequently occurs due to chemicals. Oil spills, chemical spills, or silent-oil-spills frequently impact the ecosystem.
Hence, efforts have been made to substitute petroleum resources with environmentally friendly materials representative among which are biomass-derived oils and fats.
Biomass-derived oils and fats are primary products that are obtained, for example, by planting trees, allowing the trees to bear fruits, and squeezing the fruits. Because carbon atoms of biomass-derived oils and fats come from CO2 preexisting in the Earth's atmosphere, the biomass-derived oils and fats, in contrast to fossil carbon-derived mineral oils, do not cause the addition of CO2 to the Earth's atmosphere, but rather, decrease the CO2 level of the Earth's atmosphere to contribute to the reduction of total CO2 through the Earth's self purification. Therefore, biomass-derived oils and fats beneficially function for the Earth's self purification and participate in the reduction of total CO2, which may allow bar increasing the tolerable usage of fossil fuels.
Drilling fluids were based on diesel in the past, but awareness of environmental problems has resulted in legal regulation that now requires drilling fluids to consist of 100% of environmentally friendly materials. With regard to diesels, biomass-derived, environmentally friendly diesels are also legally regulated worldwide to be used even at a rate of as low as ones %. In addition, the rate has tended to gradually increase.
A drilling fluid, also called boring mud, drilling mud, or just mud, is pumped through the drill string where it sprays out of nozzles on the drill bit in the process of drilling. The drilling fluid then mines the crushed or cut rock (cuttings) up the annular space between the drill string and the sides of the hole being drilled, up through the surface casing where it emerges back at the surface. The main functions of drilling fluids include (i) carrying out drill cuttings, (ii) keeping the drill bit and the drill siring cool, (iii) lubricating the drill string, and (iv) reacting against the infrastructural pressure of the borewell to prevent the wall of the bore well from collapsing.
Drilling fluids are largely classified into oil-based mud and synthetic-based fluid. Oil-based mud is a mud where the base fluid contains diesel oils, mineral oils, or other oils, without synthetic materials. Synthetic-based fluid is a mud where the base fluid is a synthetic oil prepared from a chemical material by reaction. For example, a synthesic-based fluid may be prepared by oligomerizing one or more olefin monomers in the presence of a metallocene catalyst (U.S. Pat. Nos. 5,198,012 and 6,054,415, and U.S. Patent Application No. 2011/0251445). In this regard, commercialized Chevron blends, prepared by a linear alpha-olefin process, are composed mainly of a mixture of 1-hexadecene (C16) and 1-octadecene (C18) with a ratio of 65/35 C16/C18 alpha-olefins.
In principle, drilling fluids should exhibit particular physical properties requisite for their functions. For example, density (specific gravity) is a physical property relevant to the function of allowing a column of the liquid to exactly mimic lithostatic stress within the ice as it varies with depth. Given a high pour point, a drilling fluid drastically increases in viscosity under low-temperature conditions (deep-sea drilling, oil drilling in polar regions, etc.) and is highly apt to excessively thickening. A drilling fluid with a low flash point retains a stability problem. Further, a drilling fluid cannot perform its inherent function of floating and transporting the cuttings to the surface when its viscosity is too low. On the other hand, an excessively high viscosity makes it difficult to pump the drilling fluid. Hence, the viscosity of the drilling fluid needs to be adjusted appropriately. However, such properties sometimes tend to counteract each other (e.g., an improvement in one property may be accompanied by the deterioration of another property), so that it is difficult for a single drilling fluid to simultaneously meet the required properties.
As regulations for drilling work conditions and environmental pollution become more stringent, drilling fluids are required not only to exhibit their inherent performances, but also to not cause problems to humans and the environment. However, conventional techniques have difficulty in minimizing negative environmental effects, such as non-biodegradability and/or toxicity. Inevitably retaining impurities of crude oil origin, such as polycyclic aromatics, transition metals, sulfur, nitrogen, halogen, etc., for example, oil-based drilling fluids require additional equipment or processing for removing such impurities. Synthetic-based drilling fluids, especially oligomerization products of olefins, have the potential problem of discharging the catalyst (e.g. boron trifluoride, etc.) used for the reaction as a toxic material. However, the United States Environmental Protection Agency (USEPA) applies strict standards to the regulation for biodegradability, sediment toxicity, heavy metal and polycyclic aromatic contents.
Various methods of manufacturing fuel oils such as gasoline or diesel from biomass are known, but applicability of biomass to drilling oil is not yet. Biomass contains few components that cause environmental pollution, and is composed exclusively of carbon, hydrogen and oxygen so that it is regarded advantageous in terms of preventing environmental pollution. Because drilling works are frequently earned out in cold regions in response to the increasing demand of crude oil, drilling fluids are required to be improved in low-temperature properties (particularly, pour point). Further, there is still a need fur an improvement in the basic properties of drilling fluids (e.g., flash point, specific gravity, viscosity, etc.).
From the initial time of their emergence, estolides were recognized as being applicable to use as lubricant oils (Group V, ester base oil) thanks to their structural characteristics. However, the triglyceride-derived estolides prepared the first time, although having a good pour point (PP 9 ˜−36° C.), were not directly availed as lubricant fluids due to their poor oxidation stability (RPVOT 29˜52 min). However, as a technique is provided for improving the oxidation stability by employing oleic acid as a feed and using partial hydrogenation and additives, there is a great likelihood that estolides will be available as raw materials for high-quality lubricant base oils and cosmetics.
Over petroleum-based Group I, Group II, and Group III base oils, conventional estolides have advantages in terms of viscosity index, oxidation stability, and heat stability, and are applicable to the production of high-quality lubricant base oils with Vis, greater than 100.
Such conventional estolides, produced for use as lubricant oils, are too large in molecular weight to function as drilling fluids. For example, their properties including viscosity at 40° C., specific gravity, flash point, etc. do not meet the standards required for drilling fluids. Conventional estolides, whether prepared directly from triglyceride or using oleic acid as a sole feed, are heavy hydrocarbons of 32 or more carbon atoms, and thus cannot be availed as diesel-like drilling fluids. General estolide products such as lubricant base oils are available as drilling fluids. However, these heavy hydrocarbons, although having good lubricant properties, are not regarded as high-quality drilling fluids due to their high frictional heat transmission and viscosity.
The technique of the present invention aims to produce a novel drilling fluid from a biomass-derived oils, which is in the form of estolide and exhibits properties similar to those of conventional drilling fluids. The estolides thus prepared can be availed as high-quality drilling fluids because they retain the excellent biodegradability and low-temperature properties of conventional estolides. When the use of mineral oil-derived drilling fluids are prohibited due to weather and environmental problems, the drilling fluids produced from biomass-derived oils or fats will act as an excellent alternative.